A command, in the most general sense, is an executable file or a shell builtin. For example, cd, ls, echo and firefox are commands. Some are simpler than others in at least two different ways. The actions of some are completely specified on the command line that invokes them like all the above list except the last one, firefox. More elaborate ones continue to interact with you after they've started, and are sometimes called applications. Many, but not all, of these applications interact through a graphical interface, or GUI.

Note: details of commands vary from version to version and available commands vary from distribution to distribution.

General notes on commands

Commands may be invoked as simple commands. In these examples, the $ that starts each line is a shell prompt and not meant to be typed

$ ls

Or they may be invoked as complex commands.

$ ls -l /bin

Here "-l /bin" are a pair of arguments (separated from each other and the command by whitespace) and "-l" is specifically an option, since it modifies the behavior of ls (it produces a long listing), while "/bin" simply specifies a target for ls to act on.

They may also be invoked in multiples where the semicolon is a command separator.

$ cd /bin; ls

That's two commands on one line. You may also execute one long command on two lines by escaping the carriage return with a backslash. (See scripting for further details on metacharacters and escaping and quoting.)

$ cd really long command line \
that we would like to finish here

Another way to invoke multiple commands is conditionally, where (in bash) "&&" means to execute the second command only if the first returns with an exit code of 0 (i.e., it succeeds).

$ cd /bin && ls

With the semicolon command separator, had the change of directory failed, ls would still have been invoked and simply listed the contents of the current directory. With the conditional operator, ls would not be invoked if cd had failed.

Similarly, "||" means to execute the second command only if the first returns a non-zero exit code (i.e., it fails).

$ cd /bing 2>/dev/null || echo 'I kinna do it, Cap'\''n!'

This will cd to the directory named "bing" if it in fact exists and the command will exit. Since it probably doesn't, being a typo, the second command will execute and print a somewhat more entertaining error message than is usual.

Learning about commands with local documentation

A Linux system should have documentation in the form of man pages and possibly GNU info pages (see also texinfo). In a manner similar to this page's alphabetical list, if you know the command you wish to learn more about,

$ man command

will show you the manual page of command.

If you do not know the command but would like to see commands relevant to a topic, use

$ apropos subject

or

$ man -k subject

to find suitable commands.

Unfortunately, while most man pages will be informative and complete, many GNU utilities distribute very sketchy man pages whose primary purpose is to redirect the user to the info system. In that case,

$ info command

will invoke that system of documentation.

Many commands have an "-h", "-H", "-help", "--help" option or some combination thereof. Unfortunately, some commands understand other things by "-h" or "-H" so unexpected and possibly unpleasant results may occur.

There are also extensive miscellaneous files usually found in /usr/doc, /usr/local/doc, /usr/src/linux/Documentation (kernel docs), and elsewhere.

Access

Man pages are monolithic and some are quite long, and it's occasionally hard to find what you want. The tradeoff is that the man command automatically puts you in a pager that allows you to search for specific text, usually using key bindings like vi. This can be good if you know what to look for.

Info pages are usually subdivided, and contain some directory and hyperlink information. The tradeoff is that you need to be at least minimally familiar with the key bindings used for navigation. They are a subset of those for emacs. Alternatively, you can export the entire tree as a single text document and view through a pager with the command

$ info --subnodes command | less

this loses the hyperlinks, but you can use the same navigation skills you use on a man page.

Lists of commands

In our Category Command you will find all commands in this wiki, but without explanation. The next chapter lists the most relevant ones with a short explanation so you can decide if the respective command is right for you. If you add to this list, your contribution should be didactic, understandable for newcomers, focused on the "real world" and contain sensible examples.

By name

This is a list of commands that gives you just enough information to decide what command you want to use.

A

alias - allows you to create shorter or more familiar names for commonly used commands
apropos - search the manual page names and descriptions
apt-get - a package management frontend for Debian-based distributions
at - execute a command-line task at a specified future time
awk - print only the n^th word of an input line and more

B

badblocks - a command disk utility
bash - a shell
beep - customized audible alerts
bg - run a process in the background
bunzip2 - unpack files packed with bzip2
bzip2 - a pack utility

C

cat - receive strings from stdin or a file and output them to stdout or a file
cd - change to directory
chgrp - change the group ownership of a file
chmod - change the permission mode of a file
chown - change the owner of a file
chroot - change the position of a root directory in filesystem
chsh - change the shell of a user
clear - clear the terminal screen
cmp - compare arbitrary files.
cp - copy a file
cpio - pack or unpack files in cpio archives or tarballs
cron - schedule tasks to be executed regularly at a specific time
crontab - control the cron service
cut - display specific coloumns of a file delimited by a character
cvs - a version management system

D

date - output or set date and time
dd - dump a disk to/from a file and more
df - show how much free disk space there is
diff - show the difference between two files and more
dig - show answer of DNS lookup of queried name server
disown - disowns a job (removes the pid of the job). Even when the shell exits, the job won't stop running
du - show how much disc space is used up

E

echo - echo a string/value to stdout
emacs - a text editor (and much more)
env - show all environment variables
exit - exit most shells
export - set an environment variable in bash and sh

F

fdisk - partition a disc
fg - fetch a process from the background to the foreground
file (command) - determine a file's type
find - find a file depending on its name, size, change date or other attributes
ftp - get files from the internet
fuser - identify processes using files or sockets

G

g++ - compile C++ code
gawk - This command is used to find text within files and replace it.
gcc - compile C code
getopts - Parse positional parameters
grep - grab for patterns in a file and more
groupadd - Use this command to add security user groups.
groupdel - This one is used for deleting a certain group.
groupmod - While the last one deletes, this one modified a group.
groups - show what groups your user is in
gunzip - unpack files from a special format
gzip - pack files in a special format

H

halt - shut down your computer
head - show only the first n lines of a file and more
hexdump - show a file's content in hexadecimal numbers and more
history (command) - show a command history in the bash shell
hostname - show your computer's name
hwinfo - show your available hardware

I

id - show your user and groups ids
ifconfig - show your ip address and more
info - show info about a given command
init - change runlevel
iptables - show your firewall configuration
iptraf - Interactive IP LAN monitor

J

jobs - gives a list of current background jobs (processes)

K

kill - kill a process
killall - kill all processes with a given name

L

ldd - show dynamic libraries needed by an executable
less - show output in a viewer where you can scroll and search
ln - link a file
ls - list files in a directory
lshal - list HAL devices
lshw - list hardware
lsmod - list loaded kernel modules
lsof - list open files and listening sockets
lspci - list all pci devices
lsusb - list usb devices

M

make - compile software and more
man - get help on commands
md5sum - compute the md5 sum of a file and more
mkdir - make a directory
mkfs - format a device
minicom - communicate over your RS232 interface
more - show input in a searchable pager
mount - prepare a device for reading and writing
mv - move a file (or rename a file)

N

netcat - Send some bytes to the network
netstat - get information on listening sockets, open ports and more
nice - set a process's priority
nm - list the names of functions in an object file
nmap - network and port scanner tool
notepad - a simple text editor, good for folks transitioning to linux, provided by wine.

O

objdump - show information about object files
openssl - create cryptographic server certificates and more

P

passwd - change user password
ping - show if a given computer is up and running
ps - show running processes
pwd - show your current working directory

Q

quota - manage how much resources the user is allowed to consume

R

rar - rar files/directories
read - read a string from your keyboard and more
reboot - reboot the computer
rename - rename a file
rm - delete a file
rmdir - remove empty directories
route - manage your network routing table
rpm - a package management backend for Redhat and Fedora
rsync - synchronize your folders over the network

S

scp - (secure copy) over a network
screen - a terminal multiplexer
sed - manipulate a stream of characters (scripting language)
setenv - change the value of an environment variable in the csh
shuf - generate random permutations
shutdown - shutdowns/reboots the system
sleep - wait/delay some time
ssh - login into / execute commands in a remote host
su - change user
sudo - execute the command as another user (usually root- /etc/sudoers)

T

tail - show only the last n lines of a file and more
tar - pack files in a special format
tcpdump - dump the tcp network traffic
tee - multiplex cli output
time - show the time needed by a command to finish
top - show the top CPU consuming processes and more
touch - create a file or update its time stamp
traceroute - show the route a packet takes over the network
tac - print the file in reverse. (opposite of cat) (cat X tac)
tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems

U

ulimit - show the limits of your user
umount - unmount a device (Often requires sudo permissions)
uname - show the running kernel's version and more
uniq - remove repeated lines in a sorted file
unrar - extract .rar files
unzip - unpack files
uptime - show the time since your computer was last switched on
useradd - add a user
userdel - delete a user
usermod - modify a user

V

Vgcreate - create lvm volume groups
Vgdisplay - display lvm volume groups
Vgs - show information about lvm volume groups
Vgscan - scan for lvm volume groups
vim - a text editor, not entirely unlike Notepad, but more powerful and programmable.
Vmstat - show input/output values, swap, memory consumption and more

W

w - print who is logged in to your system
wc - word count (word,line,char)
wget - The non-interactive network downloader
whereis - locate the binary, source, and manual page files for a command
which - print the path where you find an executable file
who - see who is on the system
whoami - print your effective user name

X

xargs - hand over stdin as a parameter
xev - show information about your keystrokes and more
xkill - kill a window that is in your way
xosview - show CPU/memory/hard Drive activity and more

Y

yes - repeatedly output a string
yum - a package management frontend for Redhat & Fedora
yast - a package management frontend for SUSE

Z

zcat - apply cat on Gzip files
zcmp - apply cmp on Gzip files
zdiff - apply diff on Gzip files
zgrep - apply grep(search in) possibly compressed files
zip - pack a file
zless - apply less on a compressed file
zmore - apply more on a compressed file

By category

Links

External Links

Command

Contents